<?php 

trait A 
{
    public static $name = '静静';
    public static function demo()
    {
        echo 'A中的demo..<br>';
    }
    abstract public function tt();
}

class User
{
    use A;
    public function tt(){}
}
User::demo();
echo User::$name;

$u = new User();
$u->demo();

echo '<hr>';